<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:mathml="http://www.w3.org/1998/Math/MathML">
      <body onload="run()">
      <mathml:math id="test" style="display: block">
      </mathml:math>
<script>
  function run() {
    var t1 = document.createElementNS("http://www.w3.org/1998/Math/MathML",
                                      "mtable");
    var t2 = document.createElementNS("http://www.w3.org/1998/Math/MathML",
                                      "mtable");
    var r1 = document.createElementNS("http://www.w3.org/1998/Math/MathML",
                                      "mtr");
    var r2 = document.createElementNS("http://www.w3.org/1998/Math/MathML",
                                      "mtr");
    var test =
      document.getElementsByTagNameNS("http://www.w3.org/1998/Math/MathML", "math")[0];
    t1.appendChild(r1);
    test.appendChild(t1);
    test.appendChild(t2);
    t2.appendChild(r2);
    
  }
</script>
</body>
</html>
